The Darwin’s rhea (Rhea pennata) is a large-bodied, flightless bird—the second largest herbivore, after the guanaco, in the Patagonian and southern Andean steppe. Although there are few good data to document their current status, populations throughout the region appear to have declined dramatically. At one site in southern Neuquén province they declined 86% in 20 years. Potential causes for the decline of the Darwin’s rhea are competition with livestock for food and water, hunting and collection of eggs, and increased predation and egg consumption by native predators that are supplemented by livestock and the exotic European hare. These large birds have large home ranges, and our analysis indicates that virtually no protected area in Argentina is large enough to harbor a demographically viable population. The species is also ecologically extinct as prey to native carnivores in most of northern Patagonia.
WCS is working with provincial government agencies to increase poaching controls, and with government partners and oil companies to close the extensive network of oil exploration trails which provide poachers with access to remote areas. We are working with herders to decrease the impact of their goats on habitat and wildlife.
Simultaneously with these conservation efforts, we are carrying out studies to generate the information needed to refine and improve them. We are evaluating the relative influence of different threats on rheas, including hunting, livestock, and predation, and assessing the nature of long-distance movements by rheas, in order to understand seasonal variations and the scale of spatial requirements. In addition, we are monitoring population trends to determine if rheas are responding to reductions in threats, as well as monitoring the threats themselves to verify that they are indeed being reduced by our actions and those of our partners.
Because it is not known exactly which threats are most affecting Darwin’s rheas or how, our approach to reversing their decline is to address the major potential threats—hunting and competition with livestock—until we can refine our actions based on better information.